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Gene transfer mechanisms in bacteria
- 1. Gene Transfer Mechanisms inBacteria Prsented by: Sanjay Kr Vishwakarma
- 2. Gene transfer mechanismsin bacteria • Conjugation: orderly, deliberate transfer of DNA from one cell to another; programmed by specialized genes and organelles. • Transformation: uptake of environmental DNA into a cell • Transduction: transfer of DNA from one cell to another mediated by a virus
- 4. Properties of genetransfer in bacteria • All are unidirectional (donor–recipient) • Recombination requires two steps: 1. Transfer of DNA into the recipient cell, forming a merozygote (various gene transfer mechanisms) 2. Crossing over that replaces a portion of the recipient genome (endogenote) with the homologous portion of the donor genome (exogenote) • Transfer is always partial
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- 6. • Direct transfervia connection tube, one-way traffic from donor cells to recipient cells. • It is not a reciprocal exchange of genetic information. • F+ cells donor cells containing F factor • F− cells recipient cells lacking F factor • Sex Pilus – connection tube
- 7. Conjugation in E.coli is based on the F (fertility) plasmid
- 8. Transfer of integratedF includes donor chromosome Unidirectional transfer Recombination Partial transfer
- 9. DNA transfer duringconjugation is time-dependent Transfer of an entire E. coli donor genome requires about 1 hour (F sequence is last to transfer) The chromosome as a time function: • Mix donor Hfr and recipient F- cells • Interrupt transfer of DNA at various times • Plate out cells to determine which genes were transferred within each timeframe
- 10. Hfr azir tonrlac+ gal+ strs X F- azis tons lac- gal- strr
- 11. Transformation DNA in theenvironment of a cell is taken into the recipient cell forming a merozygote; then recombination occurs • Competent cells: cells that take up DNA • Transformants: cells that receive genetic material • Cotransformed: cells that are transformed by two or more genes
- 13. Transduction Transduction: Transfer ofDNA from one cell to another mediated by a virus; followed by recombination to integrate the DNA into the recipient cell. • General transduction: any genes can be transferred • Specialized transduction: only a few genes can be transferred
- 15. Bacteriophages have twoalternative life cycles: lytic and lysogenic
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- 17. 1. The Hfrchromosome is transferred to the F— cell in a _____________ fashion. a) circular b) coiled c) dimer d) linear
- 18. 1. The Hfrchromosome is transferred to the F— cell in a _____________ fashion. a) circular b) coiled c) dimer d) linear Answer: d
- 19. 2. Which ofthe following is true for an Hfr X F— cross? a) frequency of recombination high, transfer of F factor low b) frequency of recombination high, transfer of F factor high c) frequency of recombination low, transfer of F factor high d) frequency of recombination low, transfer of F factor low Answer: a
- 20. 2. Which ofthe following is true for an Hfr X F— cross? a) frequency of recombination high, transfer of F factor low b) frequency of recombination high, transfer of F factor high c) frequency of recombination low, transfer of F factor high d) frequency of recombination low, transfer of F factor low Answer: a
- 21. 3. Introduction ofDNA molecules into the recipient organism is termed as ____________ a) transformation b) translation c) transduction d) transcription Answer: a
- 22. 3. Introduction ofDNA molecules into the recipient organism is termed as ____________ a) transformation b) translation c) transduction d) transcription
- 23. 4. Which ofthe following role is performed by a bacteriophage in transduction? a) vector b) donor c) recipient d) episome Answer: a
- 24. 4. Which ofthe following role is performed by a bacteriophage in transduction? a) vector b) donor c) recipient d) episome
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